The distribution of droplet sizes in a conventional reactive spray system causes both over- and under-reaction on the small and large droplets respectively. Analysis and experiments show that relatively large droplets (on the order of 0.5 mm diameter) are nearly optimal for the generation of singlet oxygen for use in a laser system. Relatively large droplets of a single diameter are deflected only a limited distance by a gas flow in the spray system reactive volume, eliminating carryover of liquid reactant into the output stream of the singlet oxygen. The small droplets in a conventional spray system are subject to massive carryover in a transverse flow system due to their low mass and relatively high frictional drag. Accordingly, it is desirable to have a spray reactive system that is capable of producing relatively large, highly uniform, droplets.